tran_getcap() is called to get the current value of a capability specific
to features provided by the HBA hardware or driver. The name of
the capability cap is the NULL terminated capability string.

If whom is non-zero, the request is for the current value of
the capability defined for the target specified by the scsi_address(9S) structure
pointed to by ap; if whom is 0, all targets are affected; else,
the target specified by the scsi_address structure pointed to by ap is
affected.

tran_setcap() is called to set the value of the capability cap to
the value of value. If whom is non-zero, the capability should be set
for the target specified by the scsi_address(9S) structure pointed to by ap;
if whom is 0, all targets are affected; else, the target specified
by the scsi_address structure pointed to by ap is affected. It is
recommended that HBA drivers do not support setting capabilities for all targets, that is,
whom is 0.